Contact lenses have been used commercially to improve vision since the 1950s. Many current contact lenses are made of hydrogels formed by polymerizing hydrophilic monomers such as hydroxyethylmethacrylate (HEMA) and vinylpyrrolidone in the presence of a minor amount of a crosslinking agent.
When producing continuous wear contact lenses, it can be advantageous to include silicone monomer in order to increase oxygen permeability in the lenses. However, as the amount of the silicone monomer in the reactive mixture is increased, dissolution with conventional solvent systems becomes more difficult and the resulting materials are typically hydrophobic.
In cases where non-aqueous solvents are used to dissolve hydrophobic materials, the solvent typically must be later removed by extraction or the like. Thus, a step of replacing the solvent with water is frequently utilized. Additionally, while some solvents can adequately dissolve silicone prepolymers, these solvents can irritate a contact lens wearer's eyes. Thus, complete removal of such a solvent becomes necessary. Moreover, some solvents (e.g., poly(ethylene glycol)) show less irritation to a contact lens wearer's eyes and provide a uniform and transparent silicone prepolymer solution. However, when polymer films prepared in such solutions are immersed in water, they become opaque. That is, polymerizations in such solvents typically result in unclear polymer films.
Therefore, there remains a need for methods and compositions that overcome these deficiencies and that effectively provide polymerization compositions wherein the monomers and/or prepolymers are soluble in water-soluble solvents and result in molded polymer films and articles exhibiting satisfactory oxygen permeability, minimal or nonexistent eye irritation, and highly transparent products.